1. Field of the Invention
The present invention relates to an imaging system and a method of driving the same and, in particular, to increase in dynamic range and improvement in S/N ratio.
2. Description of the Related Art
As to solid-state imaging devices improvement in S/N ratio and increase in dynamic range is required. Japanese Patent Application Laid-Open No. 2004-015701 describes that, for meeting such a requirement, a detection circuit for detecting the level of an image signal and an amplifier circuit are provided for each column of pixel arranged in a matrix to control the gain of the image signal on a pixel basis. This allows increase in dynamic range with the S/N ratio maintained.
Japanese Patent Application Laid-Open No. H06-070222 describes an amplifier circuit for amplifying an output signal from an imaging device. For a signal in a relatively bright area, there is performed synthesis using data in which an output signal from the imaging device is analog-to-digital converted. For a signal in a relatively dark area, there is performed inlay synthesis using data in which a signal amplified with a higher amplification ratio is analog-to-digital converted. This, according to the application, allows the effective use of dynamic range of the imaging device.
In the technique disclosed in Japanese Patent Application Laid-Open No. 2004-015701, however, the detection circuit for detecting a pixel signal from a pixel is provided for each column of pixel, increasing an area occupied by the solid-state imaging device. Furthermore, detection is performed for each pixel which leads to an increase in power consumption.
In the technique disclosed in Japanese Patent Application Laid-Open No. H06-070222, on the other hand, the S/N ratio of a signal output from the imaging device is not changed. The dynamic range of the imaging device itself is not increased either.